Slope behaviour during excavation of the Sarnia approach to the Saint Clair Tunnel

In 1889, work began on the excavation of the approach cut for the St. Clair River Tunnel in Sarnia, Ontario, Canada. Several slope failures occurred during different excavation stages before the Sarnia approach and the original tunnel project was successfully completed in 1891. In 1993 construction commenced on the new St. Clair Tunnel project. Located adjacent to the original, the new tunnel alignment made use of the existing approaches but required additional excavation to widen and deepen the original cuttings. In Sarnia, the new work initiated unusual, deep-seated deformations on the slope opposite to the slope where the new excavation occurred.; The performance of the excavated slopes over the entire history of construction at the Sarnia approach is analysed in this research using both limit equilibrium and finite element analysis. The chronology of events associated with the construction is documented and the geology and constitutive parameters for the St. Clair till stratum at the site are extensively assessed.; The construction of the original (1889 to 1891) stages of excavation at the site are numerically simulated using total stress and fully coupled, effective stress finite element (FE) formulations. For the effective stress analysis, an Elliptical Cap critical state model is shown to best describe the observed behaviour but is sensitive to several key parameters. After verifying the analytical approach for the early stages of excavation, the entire construction within the approach is numerically simulated using the Elliptical Cap model. Initial predictions are unable to capture the trend of deformations noted in the field in 1993, especially the deep-seated deformations observed on the south slope.; Investigation into the affects of the presence of ex-solved natural gases within fine grained soils indicates a potential mechanism influencing slope behaviour during unloading. A method of identifying the extent of gas permeation into the St. Clair till is discussed and an approach to modelling its effects is proposed. Incorporating gassy soil behaviour into the effective stress, finite element analysis results in substantially better predictions in the trend of slope deformations, and highlights the importance of such a mechanism not usually considered in this type of analysis.